The field of the invention relates generally to power generation systems and, more particularly, to a waste heat recovery system for use with power generation systems and a method of using waste heat.
At least some known power generation systems, such as combined-cycle systems, include an air compressor, a gas turbine engine, a heat recovery steam generator (HRSG), a steam turbine, and a gas separation system. Gases that are optimal for combustion are channeled from a gas source to the gas turbine engine to enable the gas turbine engine to generate a power output. Exhaust gases from the gas turbine engine are channeled to the HRSG, wherein the exhaust gas is converted to steam. The steam is then channeled to the steam turbine to generate power therefrom.
The gas source may also include various constituents that are not optimal for combustion, such as hydrogen sulfide gas (H2S), carbon dioxide gas (CO2), and/or nitrogen gas (N2). As such, the gases from the gas source may be channeled to the gas separation system, wherein noncombustible gases are separated from the combustible gases such that only the combustible gases are channeled to the gas turbine engine. For example, the gases may be separated via a gas separation membrane in which, depending on the type of membrane used, combustible gases, such as methane gas, are unable to pass through the membrane and become part of the retentate, and the other gases pass through the membrane and become part of the permeate.
Gases in the retentate are channeled to the gas turbine engine for use in the power generation process. In contrast, the permeate does not have an immediate use for the power generation process. However, the permeate may, in fact, contain combustible gases, such as methane gas. More specifically, known gas separation membranes used in such separation processes are not entirely selective, and allow for a portion of combustible gases to pass through the membrane. Since there is no immediate use of the permeate as part of the power generation process, combustible gases within the permeate represent a loss to the system as all available energy for power generation is not completely utilized.